Theory and troubleshooting using short modules packed with images to make learning quick and easy.
Thermistors are used to sense/measure temperature. You will find them in ductless splits to detect evaporator coil or condenser temperature, temperature measuring devices such as a digital thermostat, ambient air temperature, PTC start relay, and supply or return air temperature. The name thermistor is a combination of “thermal” and “resistor.”
Improper condensate trapping can cause a lot of property damage. It’s necessary that a drain line is installed correctly to avoid damage to a residence or business.
Evaporators coils are installed to allow a blower to either push or pull air across the coil. The pressure, either positive or negative applied across the coil is also the same applied pressure to the drain line connected to the drain pan of the evaporator coil.
The thermostat is the command center for an HVAC system. The thermostat is what will switch the equipment on and off. Most people are familiar with the thermostat on the wall for their heating and cooling, but they’re in almost everything from water heaters to freezers and kitchen equipment.
Modern thermostats sense temperature using a thermistor. The thermistors resistance value changes depending on the surrounding temperature. A small microcontroller converts the measured resistance to temperature and decides based on desired settings if heating or cooling should be switched on.
The following is an example of a 90%+ furnace. Things may differ slightly from manufacturer to manufacturer, but they’ll all be pretty close, and theory will remain the same.
The following sequence is for the Rinnai tankless water heater. If you can learn this sequence, you will have a good understanding across the board for all brands out there as they all follow a similar sequence of operation.
Step 1. Upon a call for hot water, the water flow sensor will sense water flow and send a pulsing signal to the PCB (control board). The gallons per minute minimum to start the unit start trial for ignition will differ across models and brands, but 0.4 gpm is common
You’ll run into these terminals commonly on older standing pilot furnaces. TH/TR is a common connection, but that doesn’t explain much in itself.
We’ll overview which each of these terminals is intended for:
TH – The 24v hot leg from the thermostat on a call for heat (R+W closing on the thermostat) to the gas valve (TH terminal) to open the solenoid to allow gas to flow, assuming the transformer is working and the high limit is closed (allowing for the flow of electricity)
Sheet metal box connected directly to the supply outlet of the HVAC appliance that directs the heated or cooled air to the ductwork.
Most units have multiple, or at least one return duct in the house moving conditioned room air to the HVAC unit. When air is forced through the supply ductwork, conditioned room air gets pulled throughout the structures return ductwork into the central return air plenum to be moved through the appliance to be heated or cooled.
Take any chance you have to skip connecting refrigerant gauges to a system. Each time you attach your gauges, you remove a small amount of refrigerant from the system through your hoses. The longer the hoses, the more charge that’s lost. After a few times of doing this, you might end up chasing a leak that doesn’t even exist.
Air
Aldehydes
Aldehydes are a product of incomplete combustion. They’re irritating to the eyes, throat, and nose and smell terrible. Tastes somewhat metallic and are likely accompanied by carbon monoxide
Ambient
The ambient air temperature is the dry-bulb temperature of the surrounding air
Applied voltage
The voltage supplied or applied to the electrical circuit
(also known as supply voltage)